The present invention relates to a shiftable clamping-type locking mechanism, and in particular to a locking mechanism used in gearboxes for adjusting a seat position of a car seat.
In general, clamping-type locking mechanism of this type are used to secure the position between two elements. When releasing a locking mechanism, both elements can be moved in directions that have been previously locked. The locking mechanism is provided with tracks between which clamping members are positioned and so spring-loaded against these tracks as to seek a clamped position. The tracks may, for example, be formed on opposing outer cylindrical surface areas of both elements. It is also conceivable to design the tracks along confronting sides of longitudinally displaceable elements. Locking mechanisms of this type may be installed, for example, in gearboxes in which a shaft should be securely fixed in both directions of rotation. Such gearboxes are used, for example in seat adjustments of motor vehicles or in mechanisms for raising and lowering windows in motor vehicles.
International patent publication WO 96/20352 discloses a clamping-type locking mechanism for adjusting the seat position of a seat. The locking mechanism includes two elements nested within its other, with the outer element forming a cylindrical track about its inner surface area, and with the inner element being provided with several circumferentially spaced ramps extending about the outer surface area in opposition to the cylindrical track and inclined in opposite directions. Each ramp forms with the cylindrical track a wedge-shaped clamping gap in which a clamping roller is positioned under spring tension. As the imaginary peaks of the wedge-shaped clamping gap either face one another or, as in this case, face away from one another, the clamping rollers positioned under spring tension in the clamping gap prevent a rotation of the inner element relative to the outer element in both directions of rotation. When the clamping rollers are released and thus in cleared position, only those clamping rollers are actually freed which are functionally relevant for this direction of rotation. The clamping rollers are arranged in pockets of a cage at clearance in circumferential directions, whereby the cage can be slightly pivoted relative to the inner element. This pivot path is utilized for releasing the clamping rollers from their pertaining clamping gaps. A torque acts on the inner element and is effected by a force impacting on the seat. In the clamping situation, these types of locking mechanisms retain the seat at a set level.
These types of locking mechanisms are however subject not only to static torque in their clamped position but also to oscillating, dynamic loads with changing torque. In such a changing load, the clamping force, which is transmitted from the inner element via the clamped rollers into the outer element, is initially reduced in the conventional locking mechanism, until the changing load reaches a value at least approximating zero. Although in this stage, the clamping rollers are still resiliently received in their clamping gap by means of the provided springs; However, relative movements between the inner element and the outer element are possible because of the reduced clamping action as a result of the changing load. Thus, an undesired slip may be caused. In case of a seat adjustment, such relative movements result in an unintended change of the seat level.